This invention relates to dispersions useful as slow release nitrogen fertilizers, to processes for preparing such dispersions and to their application to plants and soils. More particularly, the invention relates to dispersions formed during reactions of urea and formaldehyde, when these reactions are carried out in the presence of polyfunctional aldehydes or "polymers of formaldehyde" such as polysaccharides capable of being hydrolyzed to hydroxyaldehyde compounds. Typically, polyfunctional aldehydes may be dialdehydes of from 2 to 5 carbon atoms, hydroxyaldehydes of from 3 to 6 carbon atoms or polymers of formaldehyde such as reducible polysaccharides which form aldehydes under the reaction conditions.
In U.S. Pat. No. 4,298,512 and 4,332,610, Sartoretto and Tao, a process is described for preparing a dispersion of a urea aldehyde polymer for use in fertilizing soil wherein the process comprises reacting urea with formaldehyde and a higher aldehyde having from 2 to 4 carbon atoms such as acetaldehyde and propionaldehyde, wherein the mole ratio of formaldehyde to said higher aldehyde is at least 2:1, in aqueous solution in the presence of an acid catalyst to form a dispersion and to neutralize the dispersion.
In U.S. Pat. No. 4,033,745, to Moore, which is referred to in the prior patents mentioned above, alcohol and sugar additives including molasses are used to enhance the stability of suspensions of urea formaldehyde polymers. However the sugars used in the Moore patent are crude solutions of sucrose. The prior art has not described the use of substituted of polyfuncational aldehydes in reactions of urea and formaldehyde in the preparation of fertilizers. Sucrose, as discussed in the Moore patent, not being a disaccharide capable of acting as a reducing sugar, even upon hydrolysis, is not a sugar contemplated for use in this invention which requires aldehyde groups or the potential formation of aldehyde groups under the reaction conditions.
According to the present invention, it has been found that dialdehydes or hydroxyaldehydes may be used as chain terminators to apparently reduce the molecular weight of the polymers formed so that stable dispersions are formed which are storable for long periods of time. Various thickener-suspending agents are added to the dispersions to minimize settling. The dispersions are made water redispersible, after they are sprayed onto leaves and plants and on the soil, by the incorporation of surfactants into the dispersions.
It is an object of this invention to prepare stable, aqueous dispersions of urea-aldehyde polymers which release nitrogen to plants in a controlled manner over a relatively long period of time.
It is another object of this invention to produce dispersions of urea-aldehyde polymers which are capable of being stored for relatively long periods of time and then being readily applied to growing plants and soil without difficulty by conventional spraying equipment.
It is a further object of this invention to prepare dispersions of urea-aldehyde polymers which release nitrogen to growing plants over relatively long periods of time without causing phytotoxicity of the plants.